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The conservation and restoration of an engobed and engraved jug from the Lastovo - cap Cuf site

A large bronze vessel that contained an engraved ceramic jug with angels depicted in relief was found among other finds during underwater archaeological research in 2007 at the Lastovo, Cape Cuf, site. This kind of jug with boys or angels depicted in relief was manufactured in Venice from the late 15th to the late 16th century.

These two artefacts were completely joined by encrustations and iron oxides, the by-products of the decay of iron artefacts. The artefacts were extracted from the sea and delivered for further treatment at the Croatian Conservation Institute's Department for Conservation of Underwater Archaeological Finds in Zadar.

The artefact prior to restoration

A sherd of the ceramic jug prior to restoration

Upon their delivery the artefacts were placed in a pool where the desalinisation process began. This was followed by successive changes of the water and instrument monitoring of the water's salinity. This process was concluded when an analysis showed that most of the soluble salts had been excreted from the artefact, which allowed for the further treatment of the artefact. Subsequently, the separation of the ceramic jug from the base was undertaken, followed by its conservation and restoration.The artefacts were separated mechanically, using manual and power chisels. It was only with the separation of the large conglomeration of encrusted sea organisms and iron oxides that the original surface of the ceramic jug was revealed, whereupon it was established that it is fragmented and not in a good state of conservation. Conglomerates of petrified sea organisms and iron oxides were also present in the interior of the ceramic jug. The surface of the artefact and its fractures were dark grey to black in colour, the result of the infiltration of iron oxides into the structure of the artefact. Numerous fractures were visible on the surface of the artefact. The artefact separated along the observed fracture lines, as had been foreseen, during the process of cleaning and its separation from the bronze vessel. The remnants of iron oxides and encrustation were removed with a mechanical scalpel and power chisel.The artefact was chemically cleansed several times until most of the iron oxides were removed from the surface and structure of the artefact. Initially the artefact was immersed in a 15% solution of hydrochloric acid in water for 30 minutes. This procedure was repeated 3 times, each followed by rinsing in running water. This procedure removed much of the deposited iron oxide.This was followed by one more cleansing procedure by immersion of the artefact in a 15% solution of peroxide in water for 30 minutes. The artefact was subsequently rinsed in running water.The cleansing procedure was stopped when it was judged that most of the iron oxides had been removed and that a satisfactory colour had been attained, closest to the artefact's original colour.It was revealed that it had been coated in a white engobe under the glaze and decorated with green (copper), yellow (oxide) and brown (manganese) colour.After the completion of the cleaning process the fragments were impregnated by immersion in a 4% solution of vinyl consolidant dissolved in acetone (Mowilith).The fragments were then preliminarily joined with paper adhesive tape, followed by final gluing with the reversible ceramic glue Mecosan.The points of connection and other visible fractures were filled with alabaster gypsum. The missing section of the artefact was reconstructed with alabaster gypsum using an impression made with plasteline, where the relief decorations were also reconstructed, patterned on the existing section. The gypsum section was then toned on the pattern of the original, but using colours a nuance lighter.After the restoration intervention was completed the artefact was coated in a 3% solution of Acril 33 acrylic resin in water.The bronze vessel found with the ceramic jug is currently undergoing restoration treatment in the metal workshop of the CCI's Department for Conservation of Underwater Archaeological Finds, and is in the final phase of restoration.